Abstract:

An electrode for a super-capacitor, a super-capacitor including the
electrode, and a method of preparing the electrode in which the electrode
includes a conductive substrate; metal nano structures formed on the
conductive substrate; and a metal oxide coated on the metal nano
structures. The electrode for the super-capacitor increases the
capacitance of the super-capacitor.

Claims:

1. An electrode for a super-capacitor, the electrode comprising:a
conductive substrate;metal nano structures formed on the conductive
substrate; anda metal oxide layer formed on the metal nano structures.

2. The electrode of claim 1, wherein the metal nano structures are porous.

3. The electrode of claim 1, wherein the metal nano structures are
arranged perpendicular to the conductive substrate.

4. The electrode of claim 1, wherein each of the metal nano structures is
a metal nanorod.

5. The electrode of claim 1, wherein each of the metal nano structures is
a metal nanotube.

6. The electrode of claim 1, wherein each of the metal nano structures
comprises at least one metal selected from the group consisting of Au,
Ag, Ni, Cu, Pt, Mn, Ru, Li, and any combinations thereof.

7. The electrode of claim 1, wherein the metal oxide comprises at least
one selected from the group consisting of RuO2, MnO2,
IrO2, NiOx (0<x<2), and CoOx (0<x<2), and any
combinations thereof.

8. The electrode of claim 1, further comprising a porous polymer coated on
the metal oxide layer.

9. The electrode of claim 8, wherein the porous polymer comprises at least
one selected from the group consisting of NAFION, ACIPLEX, FLEMION, DOW,
and any combinations thereof.

10. A super-capacitor comprising the electrode of claim 1.

11. A method of manufacturing an electrode for a super-capacitor, the
method comprising:coating a first metal on a surface of a porous template
to form a first metal layer, the porous template having regularly
arranged nanopores, and the first metal layer closing ends of each of the
nanopores of the porous template;forming conducting polymer rods on the
first metal layer in the nanopores of the porous template;etching a
portion of the porous template to form spaces between the conducting
polymer rods and surfaces of the nanopores;forming metal nanotubes
comprising the first metal and a second metal in the spaces;selectively
etching the conducting polymer rods, the second metal, and the porous
template to form porous metal nanotubes formed of the first metal;
andcoating a metal oxide on the porous metal nanotubes to form a metal
oxide layer.

12. The method of claim 11, wherein the porous template is an anodic
aluminum oxide template.

13. The method of claim 11, wherein opposite ends of each of the
nanopores, the opposite ends being opposite to the ends closed by the
first metal layer, are open.

14. The method of claim 11, wherein the first metal comprises one selected
from the group consisting of Au, Ag, Ni, Cu, Pt, Mn, Ru, Li, and any
combinations thereof.

15. The method of claim 11, wherein the second metal is different from the
first metal, and comprises one selected from the group consisting of Au,
Ag, Ni, Cu, Pt, Mn, Ru, Li, and any combinations thereof.

16. The method of claim 11, wherein the conducting polymer rods comprise
at least one selected from the group consisting of polyaniline,
polythiophen, polypyrrole, and any combinations thereof.

17. The method of claim 11, wherein the metal oxide comprises at least one
selected from the group consisting of RuO2, MnO2, IrO2,
NiOx (0<x<2), CoOx (0<x<2), and any combinations
thereof.

18. The method of claim 11, further coating a porous polymer on the metal
oxide layer.

19. The method of claim 18, wherein the porous polymer comprises at least
one selected from the group consisting of NAFION, ACIPLEX, FLEMION, DOW,
and any combinations thereof.

20. The method of claim 11, further comprising, before the etching, drying
the conducting polymer rods at a temperature of about 50 to about
200.degree. C. for about 30 minutes to about 2 hours.

21. A method of manufacturing an electrode for a super-capacitor, the
method comprising:coating a first metal on a surface of a porous template
to form a first metal layer, the porous template having regularly
arranged nanopores, and the first metal layer closing ends of each of the
nanopores of the porous template;forming metal nanorods on the first
metal layer in the nanopores of the porous template;etching the porous
template; andcoating a metal oxide on the metal nanorods to form a metal
oxide layer.

22. The method of claim 21, wherein the porous template is an anodic
aluminum oxide template.

23. The method of claim 21, wherein opposite ends of each of the
nanopores, the opposite ends being opposite to the ends closed by the
first metal layer, are open.

24. The method of claim 21, wherein the first metal comprises one selected
from the group consisting of Au, Ag, Ni, Cu, Pt, Mn, Ru, Li, and any
combinations thereof.

25. The method of claim 21, wherein the metal oxide comprises at least one
selected from the group consisting of RuO2, MnO2, IrO2,
NiOx (0<x<2), CoOx (0<x<2), and any combinations
thereof.

26. The method of claim 21, further coating a porous polymer on the metal
oxide layer.

27. The method of claim 26, wherein the porous polymer comprises at least
one selected from the group consisting of NAFION, ACIPLEX, FLEMION, DOW,
and any combinations thereof.

28-30. (canceled)

Description:

CROSS-REFERENCE TO RELATED APPLICATION

[0001]This application claims the benefit of Korean Patent Application No.
10-2009-0022753, filed Mar. 17, 2009 in the Korean Intellectual Property
Office, the disclosure of which is incorporated herein by reference.

BACKGROUND

[0002]1. Field

[0003]The following description relates to an electrode for a
super-capacitor, a super-capacitor including the same, and a method of
preparing the electrode.

[0004]2. Description of the Related Art

[0005]Examples of energy storage devices using an electrochemical
principle include secondary batteries and electrochemical capacitors.
Secondary batteries have high energy density per unit weight or unit
volume, but have a short lifetime, a long charging time, and a low power
output density. Electrochemical capacitors are super-capacitors that have
a specific capacitance at least 1000 times greater than that of a
conventional electrostatic capacitor. Also, electrochemical capacitors
have a long lifetime, a short charging time, and a high power output
density, but have a low energy density.

[0006]Electrochemical capacitors can be categorized into electric double
layer capacitors, which use an electric double layer principle, and
pseudocapacitors, which use a pseudocapacitance generated by an
electrochemical Faraday's reaction. Pseudocapacitors have a specific
capacitance at least ten times greater than that of electric double layer
capacitors.

[0007]Electrodes used in pseudocapacitors include metal oxides, which
enable charging/discharging at the surface of a metal oxide layer through
an oxidation-reduction reaction. The oxidation-reduction reaction occurs
only at the surface of a metal oxides layer. Thus, when the surface area
of a metal oxide layer is larger, the metal oxide layer stores a larger
potential. Thus, an electrode that has such a structure that maximizes
the surface area of a metal oxide layer is required.

SUMMARY

[0008]Aspects of the invention provide an electrode that includes a metal
nano structure and is used in a super-capacitor, a super-capacitor
including the electrode, and a method of manufacturing the electrode.

[0009]Additional aspects will be set forth in part in the description
which follows and, in part, will be apparent from the description, or may
be learned by practice of the presented embodiments.

[0010]According to one or more embodiments, an electrode for a
super-capacitor includes a conductive substrate; metal nano structures
formed on the conductive substrate; and a metal oxide layer formed on the
metal nano structures.

[0011]According to one or more embodiments, a super-capacitor includes the
electrode for a super-capacitor.

[0012]According to one or more embodiments, a method of manufacturing an
electrode for a super-capacitor includes: coating a first metal on a
surface of a porous template to form a first metal layer, the porous
template having regularly arranged nanopores, and the first metal layer
closing ends of each of the nanopores of the porous template; forming
conducting polymer rods on the first metal layer in the nanopores of the
porous template; etching a portion of the porous template to form spaces
between the conducting polymer rods and surfaces of the nanopores;
forming metal nanotubes including the first metal and a second metal in
the spaces; selectively etching the conducting polymer rods, the second
metal, and the porous template to form porous metal nanotubes formed of
the first layer; coating a metal oxide on the porous metal nanotubes to
form a metal oxide layer.

[0013]According to one or more embodiments, a method of manufacturing an
electrode for a super-capacitor includes: coating a first metal on a
surface of a porous template to form a first metal layer, the porous
template having regularly arranged nanopores, and the first metal layer
closing ends of each of the nanopores of the porous template; forming
metal nanorods on the first metal layer in the nanopores of the porous
template; etching the porous template; and coating a metal oxide on the
metal nanorods to form a metal oxide layer.

[0014]Additional aspects and/or advantages of the invention will be set
forth in part in the description which follows and, in part, will be
obvious from the description, or may be learned by practice of the
invention.

BRIEF DESCRIPTION OF THE DRAWINGS

[0015]These and/or other aspects and advantages of the invention will
become apparent and more readily appreciated from the following
description of embodiments thereof, taken in conjunction with the
accompanying drawings of which:

[0016]FIG. 1A is a schematic diagram showing formation of an electrode
including porous gold nanotubes according to Example 1;

[0017]FIG. 1B is a schematic diagram showing formation of an electrode
including gold nanorods according to Example 7;

[0018]FIG. 2A is a field emission scanning electron microscopic (SEM)
image of porous gold nanotubes manufactured according to Example 2 before
MnO2 coating. An upper smaller image in the right side of FIG. 2A is
a reduced top view of the porous gold nanotubes, and a lower smaller
image in the right side of FIG. 2A is an enlarged image of one porous
gold nanotube;

[0019]FIG. 2B is a SEM image of porous gold nanotubes manufactured
according to Example 2 after MnO2 coating. A smaller image in the
right side of FIG. 2B is a reduced image thereof;

[0020]FIG. 2C is a SEM image of porous gold nanotubes manufactured
according to Example 2 after NAFION coating. A smaller image in the right
side of FIG. 2C is a reduced image thereof;

[0021]FIG. 2D is a SEM image of gold nanorods manufactured according to
Example 8 before MnO2 coating. A smaller image in the right side of
FIG. 2D is a reduced image thereof;

[0022]FIG. 2E is a SEM image of gold nanorods manufactured according to
Example 8 after MnO2 coating. A smaller image in the right side of
FIG. 2E is a reduced image thereof;

[0023]FIG. 2F is a SEM image of gold nanorods manufactured according to
Example 8 after NAFION coating. A smaller image in the right side of FIG.
2F is a reduced image thereof;

[0024]FIG. 3A is a cyclic voltammogram of electrodes manufactured
according to Example 2 and Comparative Example 1;

[0025]FIG. 3B is a cyclic voltammogram of electrodes manufactured
according to Example 8 and Comparative Example 2;

[0026]FIG. 4 is a graph showing galvanostatic charge/discharge test
results of electrodes manufactured according to Examples 2 and 8; and

[0027]FIG. 5 is a graph of specific capacitance with respect to the length
of a nano structure and the amount of MnO2 used of electrodes
manufactured according to Examples 1 through 12.

DETAILED DESCRIPTION

[0028]Reference will now be made in detail to the present embodiments of
the present invention, examples of which are illustrated in the
accompanying drawings, wherein like reference numerals refer to the like
elements throughout. The embodiments are described below in order to
explain the present invention by referring to the figures.

[0029]Hereinafter, an electrode for a super-capacitor, a super-capacitor
including the electrode, and a method of preparing the electrode will be
described in detail in accordance with aspects of the invention.

[0030]According to aspects, an electrode for a super-capacitor includes a
conductive substrate; metal nano structures formed on the conductive
substrate; and a metal oxide layer formed on the metal nano structures,
wherein the metal oxide layer includes a metal oxide.

[0031]In the electrode for a super-capacitor, the metal nano structures
have high conductivity and a three-dimensional nanostructure. Due to the
three-dimensional nanostructure, the metal oxide layer on the metal nano
structures may have an increased surface area. Thus, the capacitance of
the electrode is substantially increased. The metal nano structures may
be a three-dimensional nano structure.

[0032]According to aspects, the metal nano structures may be porous. Since
the metal nano structures are porous, a larger surface area is obtained
in the same volume. Thus, the metal oxide layer formed by coating a metal
oxide on the porous metal nano structures may have an increased surface
area.

[0033]According to aspects, the metal nano structures may be arranged
perpendicular to the conductive substrate. When the metal nano structures
are arranged perpendicular to the conductive substrate, the number of
metal nano structures disposed in a unit area of the conductive substrate
may be increased. Thus, the amount of the metal oxide present in the unit
area of the conductive substrate may also be increased.

[0034]In the electrode, the metal nano structures may be a metal nanorod,
a metal nanotube, or a mixture thereof. The metal nanorod or the metal
nanotube may be porous. For example, the metal nanotube may contain a
plurality of pores or apertures passing through outer and inner walls of
the metal nanotube. Thus, the porous metal nanotube may have a
cylindrical mesh structure.

[0035]In the electrode, the metal nano structures may include at least one
metal selected from the group consisting of Au, Ag, Ni, Cu, Pt, Ru, Mn,
and Li, and any combinations thereof. Aspects are not limited thereto
such that the metal nano structures may include any metal that has high
conductivity.

[0036]In the electrode, the metal oxide may include at least one metal
oxide selected from the group consisting of RuO2, MnO2,
IrO2, NiOx (0<x<2), and CoOx (0<x<2), and any
combinations thereof. RuO2 has a high capacitance of 720/g, but is
expensive. MnO2 has a relatively low capacitance, but is
inexpensive.

[0037]The electrode may further include a porous polymer coated on the
metal oxide layer. The porous polymer may be a binder that allows the
metal oxide to be stably fixed to the metal nano structures. Accordingly,
the porous polymer may improve durability and rigidity of the electrode
for a super-capacitor. In addition, due to the porous characteristic of
the porous polymer, the metal oxide may be directly exposed to an
electrolytic solution. The porous polymer coated on the metal oxide layer
may include at least one selected from the group consisting of
NAFION®, ACIPLEX®, FLEMION®, and DOW®, and any
combinations thereof.

[0038]A super-capacitor according to aspects includes the electrode
described above. Due to the inclusion of the electrode described above,
the super-capacitor may have an increased capacitance.

[0039]The super-capacitor may include a cathode, an anode, an electrolytic
solution, and a separator. The cathode may be the electrode according to
aspects. The anode may be the same as or different from the cathode.

[0040]The electrolytic solution includes a solvent and the solvent may
include at least one solvent selected from the group consisting of
acetonitril, dimethylketone, and propylenecarbonate, and any combinations
thereof, but aspects are not limited thereto. The electrolytic solution
includes an electrolyte and the electrolyte may be an alkali metal salt
that has solubility of about 0.01 mole/L or more with respect to the
solvent and is electrically inactive within an operating voltage range of
the super-capacitor. For example, the electrolyte may be lithium
percolate, lithium tetrafluoroborate, or lithium hexafluorophosphate, and
any combinations thereof, but aspects are not limited thereto. The
electrolytic solution may further include an additive for improving the
properties of the super-capacitor. Examples of the additive may include a
stabilizer or a thickener.

[0041]The separator may be disposed between the cathode and the anode so
as to divide an inner space of the super-capacitor and prevent
short-circuits between the cathode and the anode.

[0042]A method of manufacturing an electrode for a super-capacitor,
according to aspects, includes: coating a first metal on a surface of a
porous template to form a first metal layer, the porous template having
regularly arranged nanopores, and the first metal layer closing ends of
each of the nanopores of the porous template; forming conducting polymer
rods on the first metal layer in the nanopores of the porous template;
etching a portion of the porous template to form spaces between the
conducting polymer rods and surfaces of the nanopores; forming metal
nanotubes including the first metal and a second metal in the space;
selectively etching the conducting polymer rods, the second metal, and
the porous template to form porous metal nanotubes formed of the first
metal; and coating a metal oxide on the porous metal nanotubes to form a
metal oxide layer.

[0043]In the methods, each of the nanopores of the porous template may be
in the form of a channel. In other methods, a nanopore may be a nanopore
channel that extends through opposite ends of the template (see FIGS. 1A
and 1B).

[0044]In forming nanotubes as shown in FIG. 1A, a first metal layer may be
formed on a surface of the porous template having the nanopores by
thermal deposition or electroplating. An end of each of the nanopores may
be closed by filling any possible empty space or micropores of the first
metal layer by electroplating. Then, the micropores of the porous
template having the surface on which the first metal layer is formed are
filled with conducting polymer rods that grow along the micropores of the
porous template (for example, polyaniline (PANI) Deposition as shown in
FIG. 1A). The conducting polymer rods are formed using an electrochemical
synthesis method. A portion of the porous template may be etched to form
spaces between the conducting polymer rods and surfaces of the nanopores.
Before the etching, the conducting polymer rods are formed and then dried
at a temperature of about 50 to about 200° C. for about 30 minutes
to about 2 hours, thereby reducing the volume of the conducting polymer
rods. Thus, space between the conducting polymer rods and the surfaces of
the nanopores may be partially formed. During the drying, solvent and
unreacted monomers in the conducting polymer rods are removed, and thus,
the volume of the conducting polymer rods is reduced as shown in FIG. 1A
as Drying and Space Widening. Metal nanotubes formed of the first metal
and the second metal may fill the space formed by the etching by
performing an electroplating process with a mixed solution including the
first metal and the second metal (for example, Au/Ag Deposition in FIG.
1A). Then, the conducting polymer rods and the second metal are
selectively etched (for example, PANI and Ag Dissolution in FIG. 1A) and
the porous template is selectively etched (for example, AAO Dissolution
in FIG. 1A) to form porous metal nanotubes that are formed of the first
metal and are arranged perpendicular to the first metal layer. The porous
metal nanotubes are coated with a metal oxide (for example, the MnO2
Coating of FIG. 1A), thereby forming an electrode for a super-capacitor
including the porous metal nanotubes. Further, the metal oxide coated,
porous metal nanotubes may be coated with a porous polymer (for example,
NAFION Coating in FIG. 1A).

[0045]A method of manufacturing an electrode for a super-capacitor,
according to aspects, includes: coating a first metal on a surface of a
porous template to form a first metal layer, the porous template having
regularly arranged nanopores, and the first metal layer closing ends of
each of the nanopores of the porous template; forming metal nanorods on
the first metal layer in the nanopores of the porous template; etching
the porous template; and coating a metal oxide on the metal nanorods to
form a metal oxide layer.

[0046]As shown in FIG. 1B, the method may be used to manufacture an
electrode for a super-capacitor including metal nanorods. The first metal
layer may be formed on a surface of the porous template having the
nanopores by thermal deposition or electroplating so as to close one end
of the nanopores. Then, metal nanorods formed of the first metal are
formed along the nanopores of the porous template by electroplating (for
example, Au Depo. in FIG. 1B). Then, the porous template is etched (for
example, Template Dissol. in FIG. 1B), thereby forming metal nanorods
that are arranged perpendicular to the first metal layer and are formed
of the first metal (for example, Au Nano Rods in FIG. 1B). The metal
nanorods are coated with a metal oxide, thereby forming an electrode for
a super-capacitor including the metal nanorods (for example, MnO2
Coating in FIG. 1B). Further, the metal oxide coated metal nanorods may
be coated with a porous polymer (for example, NAFION Coating in FIG. 1B).

[0047]In addition, in the method of manufacturing an electrode for a
super-capacitor including metal nanorods, each of the metal nanorods may
include at least two kinds of metals. When a metal nanorod formed of at
least two kinds of metals is etched to remove one kind of metal contained
therein, an electrode for a super-capacitor including porous metal
nanorods is formed.

[0048]In the methods of manufacturing an electrode for a super-capacitor,
according to aspects of the invention, the porous template may be an
anodic aluminum oxide template. Also, nanopores formed in the anodic
aluminum oxide template may contain open opposite ends. Thus, the anodic
aluminum oxide template may contain a plurality of nanopores that extends
through opposite surfaces of the anodic aluminum oxide template.

[0049]In the methods of manufacturing an electrode for a super-capacitor,
the first metal may be one selected from the group consisting of Au, Ag,
Ni, Cu, Pt, Ru, Mn, and Li, and any combinations thereof. The second
metal may be different from the first metal and may be one selected from
the group consisting of Au, Ag, Ni, Cu, Pt, Ru, Mn, and Li, and any
combinations thereof.

[0050]In the method of manufacturing an electrode for a super-capacitor,
the conducting polymer may include at least one selected from the group
consisting of polyaniline, polythiophen, and polypyrrole, and any
combinations thereof, but aspects are not limited thereto. The conducting
polymer may be any conducting polymer that is synthesized using an
electrochemical method.

[0051]In the methods of manufacturing an electrode for a super-capacitor,
according to the above embodiments, the metal oxide may include at least
one selected from the group consisting of RuO2, MnO2,
IrO2, NiOx (0<x<2), and CoOx (0<x<2), and any
combinations thereof, but is not limited thereto.

[0052]The methods of manufacturing an electrode for a super-capacitor,
according to aspects, may further include coating a porous polymer on the
metal oxide layer. The porous polymer may include at least one selected
from the group consisting of NAFION®, ACIPLEX®, FLEMION®, and
DOW®, and any combinations thereof, but is not limited thereto, and
may be any polymer that is porous and conductive.

[0053]Hereinafter, one or more embodiments will be described in detail
with reference to the following examples. However, these examples are not
intended to limit the purpose and scope of the one or more embodiments.

[0054]Manufacturing of Electrode Including Porous Metal Nanotubes

EXAMPLE 1

[0055]A porous AAO template (Anodic Aluminum Oxide Template, Whatmann
International Ltd.) having the entire diameter of 25 mm and containing a
plurality of pore channels each having a diameter of 300 nm was provided.
Gold (Au) was deposited on a surface of the porous AAO template to form
an Au layer having a thickness of 200 nm to close ends of the pores of
the porous AAO template and form a conductive substrate.

[0056]Then, an Au solution (Ortemp 24 RTU, Technic, Inc.) was charged into
an electropolymerization apparatus (Auto Lab, PGSTAT100) including a
potentiostat and the porous AAO template having the surface on which the
Au layer was formed was dipped in the Au solution. Then, 0.8 C/cm2
of charge was applied for 10 minutes to the porous AAO template by the
electropolymerization apparatus, wherein a platinum mesh was used as a
counter electrode and an Ag/AgCl electrode was used as a reference
electrode at a constant voltage of -0.95 V vs. Ag/AgCl, thereby closing
one end of each of the pore channels with an Au film. Then, the resultant
structure was dipped in an electropolymerization apparatus (AutoLab,
PGSTAT100) charged with a mixed solution including 0.5M sulfuric acid and
0.1M aniline and cyclic voltammetry was repeatedly performed 80 times in
the range of about +1.2V to about -0.2V at a scan rate of 50 mV/s,
thereby polymerizing polyaniline in a rod-shape along the longitudinal
direction of the respective pore channels of the porous AAO template
(PANI deposition in FIG. 1A). The polymerized polyaniline contained a
solvent and unreacted monomers. The porous AAO template containing pores
filled with the polymerized polyaniline was dried at a temperature of
80° C. for 1 hour, thereby removing the solvent and unreacted
monomers. Due to the drying, spaces between the polyaniline rods and
surfaces the pores of the AAO template were partially formed (Drying and
Space Widening in FIG. 1A). The dried template was placed in a 1M sodium
hydroxide aqueous solution to etch the AAO template for 7 minutes,
thereby widening the spaces between the polyaniline rods and the surfaces
of the pores of the AAO template (Drying and Space Widening in FIG. 1A).
Then, 0.25 ml of a solution including 0.25M Na2Co3 and 0.05M
KAu(CN)2 and 0.25 ml of a solution including 0.25M Na2Co3
and 0.05M KAg(CN)2 were charged into an electropolymerization
apparatus (Auto Lab, PGSTAT100) including a potentiostat and the
resultant template in which the spaces were formed between nanopore
channels and the polyaniline rods was dipped therein. A charge of 1
C/cm2 was applied for 25 minutes to the resultant template by the
electropolymerization apparatus, wherein a platinum mesh was used as a
counter electrode and an Ag/AgCl electrode was used as a reference
electrode, at a constant voltage of -0.95 V vs. Ag/AgCl. As a result,
metal nanotubes including Au and Ag in a mole ratio of 3:1 were formed in
the space between the polyaniline rods and the surfaces of the pores
(Au/Ag Deposition in FIG. 1A). Then, polyaniline and Ag were selectively
removed with a concentrated nitric acid (PANI and Ag Dissolution in FIG.
1A). The AAO template was etched using a 3M sodium hydroxide solution and
then washed with distilled water until the pH of the distilled water used
in washing was 7, thereby obtaining porous Au nanotubes that are arranged
perpendicular to the Au layer (AAO Dissolution in FIG. 1A). The height of
the porous Au nanotubes was 2 μm. Then, a mixed solution including
0.5M sulfuric acid and 0.1M MnO2 KAu(CN)2 was charged into an
electropolymerization apparatus (Auto Lab, PGSTAT100) including a
potentiostat and the porous Au nanotubes were dipped therein. Then, a
charge of 0.05 C/cm2 was applied for 30 minutes to the porous Au
nanotubes by the electropolymerization apparatus, wherein a platinum mesh
was used as a counter electrode and an Ag/AgCl electrode was used as a
reference electrode at a constant voltage of +1.15 V vs. Ag/AgCl. As a
result, the porous Au nanotube was coated with MnO2 (MnO2
Coating in FIG. 1A). 1.8 mM NAFION (produced by Aldrich) ethanol solution
20 μL/cm2 was applied to the porous Au nanotube coated with
MnO2 and then dried at room temperature, thereby obtaining an
electrode for a super-capacitor (NAFION Coating of FIG. 1A). The weight
of coated MnO2 per 1 cm2 of the electrode was 0.05 mg.

EXAMPLE 2

[0057]An electrode was formed in the same manner as in Example 1, except
that the conditions were changed such that the height of porous Au
nanotubes was 4 μm.

EXAMPLE 3

[0058]An electrode was formed in the same manner as in Example 1, except
that conditions were changed such that the height of porous Au nanotubes
was 6 μm.

EXAMPLE 4

[0059]An electrode was formed in the same manner as in Example 1, except
that conditions were changed such that the weight of coated MnO2 per
1 cm2 of the electrode was 0.1 mg.

EXAMPLE 5

[0060]An electrode was formed in the same manner as in Example 1, except
that conditions were changed such that the weight of coated MnO2 per
1 cm2 of the electrode was 0.1 mg and the height of the porous Au
nanotubes was 4 μm.

EXAMPLE 6

[0061]An electrode was formed in the same manner as in Example 1, except
that conditions were changed such that the weight of coated MnO2 per
1 cm2 of the electrode was 0.1 mg and the height of the porous Au
nanotubes was 6 μm.

[0062]Manufacturing of Electrode Including Metal Nanorods

EXAMPLE 7

[0063]A porous AAO template (Anodic Aluminum Oxide Template, Whatmann
International Ltd.) having the entire diameter of 25 mm and containing a
plurality of pore channels each having a diameter of 300 nm was provided.
Gold (Au) was deposited on a surface of the porous AAO template to form
an Au layer having a thickness of 200 nm to close ends of the pores of
the porous AAO template and form a conductive substrate.

[0064]Then, an Au solution (Ortemp 24 RTU, Technic, Inc.) was charged into
an electropolymerization apparatus (Auto Lab, PGSTAT100) including a
potentiostat and the porous AAO template having the surface on which the
Au layer was formed was dipped in the Au solution. Then, a charge of 2.3
C/cm2 was applied for one hour to the porous AAO template by the
electropolymerization apparatus, wherein a platinum mesh was used as a
counter electrode and an Ag/AgCl electrode was used as a reference
electrode, at a constant voltage of -0.95 V vs. Ag/AgCl, thereby forming
Au nanorods integrally formed with the Au layer deposited on the surface
of the porous AAO template (for example, Au Depo. as shown in FIG. 1B).
The Au nanorods were dipped in a 3M NaOH solution for 10 minutes to etch
the porous AAO template (for example, Template Dissol. as shown in FIG.
1B), thereby manufacturing an electrode for a super-capacitor including
Au nanorods which are arranged perpendicular to the Au layer. The height
of the Au nanorods was 2 μm.

[0065]MnO2 and NAFION were sequentially coated on the Au nanorods in
the same manner as in Example 1 (for example, MnO2 Coating and
NAFION Coating as shown in FIG. 1B). The weight of coated MnO2 per 1
cm2 of the electrode was 0.05 mg.

EXAMPLE 8

[0066]An electrode was formed in the same manner as in Example 7, except
that conditions were changed such that the height of the Au nanorods was
4 μm.

EXAMPLE 9

[0067]An electrode was formed in the same manner as in Example 7, except
that conditions were changed such that the height of the Au nanorods was
6 μm.

EXAMPLE 10

[0068]An electrode was formed in the same manner as in Example 7, except
that conditions were changed such that the weight of coated MnO2 per
1 cm2 of the electrode was 0.1 mg.

EXAMPLE 11

[0069]An electrode was formed in the same manner as in Example 7, except
that conditions were changed such that the weight of coated MnO2 per
1 cm2 of the electrode was 0.1 mg and the height of the Au nanorods
was 4 μm.

EXAMPLE 12

[0070]An electrode was formed in the same manner as in Example 7, except
that conditions were changed such that the weight of coated MnO2 per
1 cm2 of the electrode was 0.1 mg and the height of the Au nanorods
was 6 μm.

COMPARATIVE EXAMPLE 1

[0071]An electrode was formed in the same manner as in Example 2, except
that MnO2 and NAFION were not coated on the porous Au nanotubes. As
a result, an electrode including porous Au nanotubes that were arranged
perpendicular to the Au layer were not coated with MnO2 and NAFION
was obtained.

COMPARATIVE EXAMPLE 2

[0072]An electrode was formed in the same manner as in Example 8, except
that Au nanorods were not coated with MnO2 and NAFION. As a result,
an electrode including Au nanorods that were arranged perpendicular to
the Au layer and were not coated with MnO2 and NAFION was obtained.

EVALUATION EXAMPLE 1

Transmission Electron Microscopy (TEM) Test

[0073]Images of the porous Au nanotubes manufactured according to Example
2 were obtained before MnO2 coating (FIG. 2A), after MnO2
coating (FIG. 2B), and after NAFION coating (FIG. 2C).

[0074]Images of the Au nanorods manufactured according to Example 8 were
obtained before MnO2 coating (FIG. 2D), after MnO2 coating
(FIG. 2E), and after NAFION coating (FIG. 2F).

[0075]Referring to FIGS. 2A through 2C, it is seen that Au nanotubes were
porous. On the other hand, the Au nanorods shown in FIGS. 2D through 2F
were not porous.

EVALUATION EXAMPLE 2

Cyclic Voltammetry Test

[0076]Cyclic voltammetry was performed on an electrode including the
porous Au nanotubes manufactured according to Example 2 (coated with
MnO2) and an electrode including the porous Au nanotubes
manufactured according to Comparative Example 1 (not coated with
MnO2) to identify a current change with respect to a voltage change.
The results are shown in FIG. 3A.

[0077]Cyclic voltammetry was performed on an electrode including the Au
nanorods manufactured according to Example 8 (coated with MnO2) and
an electrode including the Au nanorods manufactured according to
Comparative Example 2 (not coated with MnO2) to identify a current
change with respect to a voltage change. The results are shown in FIG.
3B.

[0078]In these experiments, a counter electrode was a platinum mesh, a
reference electrode was Ag/AgCl, an electrolyte was a 1M sulfuric acid
aqueous solution, and potentiostat (AutoLab, PGSTAT100) was used.

[0079]Referring to FIGS. 3A and 3B, the electrodes manufactured according
to Examples 2 and 8, which were coated with MnO2, generated more
current than the electrodes manufactured according to Comparative
Examples 1 and 2, which were not coated with MnO2. That is, when
coated with MnO2, more charge could be stored in the electrode.

EVALUATION EXAMPLE 3

Galvanostatic Charge/Discharge Test

[0080]The galvanostatic charge/discharge test was performed on the
electrodes manufactured according to Examples 2 and 8 using the MnO2
and NAFION-coated electrodes manufactured according to Examples 1 through
12 as a working electrode, platinum mesh as a counter electrode, Ag/AgCl
as a reference electrode, 1M sulfuric acid aqueous solution as an
electrolyte, and a potentiostat (AutoLab, PGSTAT100). The results are
shown in FIG. 4.

[0081]For Examples 1 through 12, a capacitance per MnO2 unit weight
was measured using a slope of a voltage curve of FIG. 4 during
discharging and the weight of MnO2. The results are shown in FIG. 5.

[0082]Referring to FIG. 5, the longer the length of a nano structure, the
higher electric capacitance, and porous Au nanotubes had a higher
capacitance than Au nanorods. When the amount of MnO2 coated was
greater than 0.05 mg, the capacitance was not further increased since
some part of MnO2 was not exposed.

[0083]As described above, according to the one or more of the above
embodiments, due to use of a metal nano structure-containing electrode,
the capacitance of the super-capacitor can be increased.

[0084]Although a few embodiments of the present invention have been shown
and described, it would be appreciated by those skilled in the art that
changes may be made in this embodiment without departing from the
principles and spirit of the invention, the scope of which is defined in
the claims and their equivalents.